Selected other vaccine studies
Breakthrough infections corelate with levels of neutralising antibodies
This paper reports 39/1497 breakthrough infections in fully vaccinated heath workers in Israel were lower compared to unvaccinated controls (ratio: 0.36; 95%CI: 0.16 to 0.78). Most had mild/moderate symptoms but 19% lasted >6 weeks. The inverse correlation with levels of neutralising antibodies suggests these levels might be a valid marker of therapeutic vaccine efficacy.
Ref: Bergwerk M et al. Covid-19 breakthrough infections in vaccinated health care workers. NEJM. DOI: 10.1056/NEJMoa2109072. (28 July 2021).
Vaccine efficacy reduced against Delta virus
Being fully vaccinated still significantly reduces risk of symptomatic infection and hospitalisation from the Delta variant. However, the lower potency might be clinically more significant in vulnerable groups who generates lower levels of neutralising antibodies.
“Sera from convalescent patients collected up to 12 months post symptoms were 4 fold less potent against variant Delta, relative to variant Alpha (B.1.1.7). Sera from individuals having received one dose of Pfizer or AstraZeneca vaccines barely inhibited variant Delta. Administration of two doses generated a neutralising response in 95% of individuals, with titers 3 to 5 fold lower against Delta than Alpha.”
Ref: Planas D et al. Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization. Nature. doi: 10.1038/s41586-021-03777-9. (29 June 2021).
Antibody responses and likely duration of protection
Complex study comparing antibody responses from seven phase 3 vaccine and convalescent cohort studies that estimate neutralisation levels and model duration of protection. Correlates early efficacy with durability to estimate importance and timing of booster doses.
Ref: Khoury DS et al. Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection. Nature Medicine 27:1205–1211. (17 May 2021).
Data review from mixing vaccines
A review article in Nature for results from five studies that have used mixed vaccine strategies.
“…a least 16 vaccines have been approved for use in one or more countries, and mix-and-match studies so far have been small, so more extensive trials and long-term monitoring for side effects are sorely needed.”
Ref: Lewis D. Mix-and-match COVID vaccines: the case is growing, but questions remain. Nature 595, 344-345. (1 July 2021).
Vaccines generate long-term immune responses
“ Our studies demonstrate that SARS-CoV-2 mRNA-based vaccination of humans induces a persistent germinal centre B cell response, which enables the generation of robust humoral immunity.”
“…In this study, we show SARS-CoV-2 mRNA vaccine-induced germinal centre B cells are maintained at or near peak frequencies for at least 12 weeks after secondary immunization.”
Ref: Turner JS et al. SARS-CoV-2 mRNA vaccines induce persistent human germinal centre. Nature. (28 June 2021).
Review of Sputnik V vaccine studies
A review of accumulated evidence from the Russian Spuknik V vaccine, which is so far neither EMA nor WHO approved. Sputnik V uses two different adenoviruses, for the first and second dose (rAd26 and rAd5, respectively).
Sputnik has already been used in some country vaccine programmes including Russia, Argentina, Hungary, Iran and Brazil and it is also being manufactured in South Korea, Argentina and India.
Other studies are still ongoing, including in the UK.
Ref: Mounting evidence suggests Sputnik COVID vaccine is safe and effective.
Second doses evens out responses in vulnerable groups
Significant differences in antibody levels following a single dose were reported, including by age, comorbidity and use of immunosuppressive therapy.
However, these difference largely resolved in all groups following a second dose, with antibody titres above the minimum target of 250 U/mL observed for nearly all people across all ages, demographics, and clinical groups.
The main group still reporting significantly lower responses (approximately 80% protected) were people with a history of haematological cancer. Antibody titres were also lower in people on immunosuppressive therapy. The study included 9 HIV positive people, but without CD4 details.
The study included 8,517 vaccinated participants (median age 65 years [IQR: 58, 71]). Approximately 60% used the Oxford vaccine and 40% Pfizer.
Ref: Shrotri M et al. Spike-antibody responses following first and second doses of ChAdOx1 and BNT162b2 vaccines by age, gender, and clinical factors – a prospective community cohort study (Virus Watch). Medrxiv pre-print, 2021.05.12.21257102v2. (15 May 2021).
This report was first posted on 25 July 2021.